Aberrant methylation of hMLH1 and p16INK4a in Tunisian patients with sporadic colorectal adenocarcinoma.

The methylation of CpG islands in the promoters is associated with loss of protein via repression of gene transcription. Several studies have demonstrated that tumour suppressor and DNA repair genes are often aberrantly hypermethylated in colorectal cancer. The present study was conducted to examine whether the methylation profile of p16INK4a and hMLH1 (human mutL homologue 1) promoters was associated with clinical features and patients' survival in CRC (colorectal carcinoma). Aberrant methylation of p16INK4a and hMLH1 promoters was found in 47.2 and 53.4% of tumours respectively. For adjacent non-tumoral mucosa, p16INK4a was fully unmethylated in 30% of the cases, whereas hMLH1 was predominantly unmethylated (76%). Methylation of p16INK4a correlated with gender and tumour size (P=0.005 and 0.035 respectively), whereas those of hMLH1 significantly correlated with overall survival (P log rank=0.007). Concomitant methylation of p16INK4a and hMLH1 was associated with TNM (tumour, lymph node and metastases) stage and tumour size (P=0.024 and 0.021 respectively). Our data show that loss of hMLH1 expression through aberrant methylation could be used as a marker of poor prognosis in CRC.